Vacuum pumping arrangements used to pump fluid from semiconductor tools typically employ, as a backing pump, a multi-stage positive displacement pump employing inter-meshing rotors. The rotors may have the same type of profile in each stage or the profile may change from stage to stage.
During semiconductor processes such as chemical vapour deposition processing, deposition gases are supplied to a process chamber to form a deposition layer on the surface of a substrate. As the residence time in the chamber of the deposition gas is relatively short, only a small proportion of the gas supplied to the chamber is consumed during the deposition process. Consequently, unconsumed gas molecules pumped from the chamber by a vacuum pump can pass through the pump in a highly reactive state. As a result, pump components can be subjected to damage due to corrosion and degradation resulting from the pumping of aggressive, unconsumed gas molecules. Furthermore, if the unconsumed process gas or by-product is condensable, sublimation on lower temperature surfaces can result in the accumulation of powder or dust within the pump, which can effectively fill the vacant running clearance between the rotor and stator elements of the pump. Other processes use gases that can result in potentially flammable mixtures forming in the pump.
To dilute these gases as they pass through the pump, an inert purge gas, such as nitrogen, can be supplied to the pump. As this gas can also serve to increase the longevity and effectiveness of dynamic shaft seals of the pump, and can ensure that certain sensors within the pumping arrangement are maintained in a clean and functional state, it is typically supplied through a plurality of purge ports provided at various locations about the pumping arrangement.
FIG. 1 illustrates a typical system for supplying purge gas to a number of purge ports. The system 10 comprises a manifold 12 having an inlet 14 and a plurality of outlets 16. The inlet 14 is connected to a source 18 of purge gas, such as nitrogen or helium, via a conduit 20, which includes a check valve 22. As the pressure of the purge gas at the source 18 may be variable, for example, within the range from 20 to 100 psi, the conduit 20 also includes a pressure regulator 24 for adjusting the pressure of the stream of purge gas conveyed to the inlet 14.
Within the manifold 12, the received stream of purge gas passes through a mass flow transducer 26 before being split into a plurality of streams for conveyance to the outlets 16. As the flow requirement at each outlet 16 may be different, depending on the purpose for which the purge gas is being supplied to a particular purge port of the pumping arrangement, the manifold 16 contains a relatively expensive arrangement of solenoid valves 28, fixed flow restrictors 30 and variable flow restrictors, for example needle valves, 32 for adjusting the flow rate of each stream of purge gas supplied to an outlet 16. Whilst the variable flow restrictors 32 can be replaced by relatively cheaper orifice plates as fixed flow restrictors, these are required to be machined to a very high accuracy which is difficult to achieve in practice, and in such systems several orifice plates are often modified during installation of the gas supply system to achieve the required flow rates to the manifold outlets.
The system 10 is typically connected to a pumping arrangement using rigid, usually stainless steel, pipes 34 of 4-5 mm internal diameter. These connecting pipes can undesirably transfer vibrations from the pumping arrangement to the gas supply system. Furthermore, the system is typically supplied with different sets of connecting pipes to enable the system to be connected to a range of different pumping mechanisms, which can significantly increase costs.
In at least its preferred embodiment, the present invention seeks to solve these and other problems.